Solid ones, in a newer resin, work just fine, much to my surprise! I too expected the assembly to require metal somewhere in the wing struts, and I did investigate getting some bespoke tubing rolled to the correct profile. This was doable apparently, and the cost per metre was fine. However, the minimum run they were prepared to do was....... 5 kilometres of the stuff!! So, back to the drawing board. Hence the metal tubing in the current kits, which was a painful compromise, I know! But very sturdy. Anyway, with a bit of encouragement, and against my better judgement, and, to be fair, the arrival of an apparently more suitable resin, I gave the printing route a try, and after a tiny bit of adjustment in both geometry and processing, they work! So, from now on, kits will come with resin struts, and I'll be sending out sets to those customers who already have the kit.
In the meantime, I don't think I have had as much fun doing research for a product as this....